This invention relates to apparatus and techniques for storing and reproducing information and, more particularly, to a system for storing and reproducing television information using video disks which can be replicated in relatively large quantities.
The recording of television information on storage media for use by the public has become relatively widespread in recent years with the advent of video tape recording equipment for the consumer. However, it has been recognized that existing video tape systems have drawbacks of complexity and expense which limit their appeal. The cost of the magnetic tape itself is considerable, and magnetic tape also has the drawbacks of slow access to the information stored therein and the need for rewinding the tape before it is replayed. In response to these deficiencies, various proposals have been set forth for recording television information on "video disks" which are to be played in the general manner of a phonograph recording; i.e., using a turntable and pickup device, typically mounted on a pivot arm. The video disk generally has advantages of relatively low cost, easy replication, fast access to all information thereon, and no necessity of rewind. Data can be recorded on the disk by various techniques, for example by modulation of the optical properties or of the electrical capacitance at the disk surface. The following U.S. patents illustrate representative prior art techniques:
U.S. Pat. No. 3,287,563 PA1 U.S. Pat. No. 3,501,586 PA1 U.S. Pat. No. 3,624,284 PA1 U.S. Pat. No. 3,795,902 PA1 U.S. Pat. No. 3,806,643 PA1 U.S. Pat. No. 3,939,302 PA1 U.S. Pat. No. 3,975,630 PA1 U.S. Pat. No. 4,001,494 PA1 U.S. Pat. No. 4,015,285 PA1 U.S. Pat. No. 4,021,606 PA1 U.S. Pat. No. 4,025,731
Since the information being recorded includes relatively wideband video signals, and the recording disk is of limited area, designers have struggled with the problem of compressing enough information onto the record disk to obtain a reasonably long program playing time for the disk. As the data is compressed, the tasks of precisely tracking the data regions on the disk and of recovering the information therein, give rise to further difficult problems.
In the U.S. Pat. No. 3,939,302 there is disclosed apparatus for recording and reproducing a video signal on a photographic record disk. Composite television signals are recorded in a spiral track or in a series of concentric circular tracks on a record disk. Each track consists of line sequential signals optically recorded in the radial direction on the disk with each radially oriented optical track representing one horizontal scanline of the television signal, so that successive scanlines are arranged in the circumferential direction of the track. The disk is mounted on a turntable which is precisely rotated at an "extremely low speed" while a video signal reproducing head optically follows the spiral or concentric tracks on the record. A photo-detecting assembly includes an optical shutter that operates in a manner similar to a Nipkow disk and has a number of small apertures therein arranged in a circle. The Nipkow disk is rotated at a constant speed and the turntable is rotated independently at a variable speed to account for the different data density at different disk radii. The photo-detecting assembly is moved radially with respect to the disk, either by moving the assembly itself or laterally moving the disk turntable.
While there are some advantages to the approach taken in the U.S. Pat. No. 3,939,302, a number of operational problems could stand improvement, some of which are as follows: The variable speed turntable drive is complex and expensive. Even a small error in turntable speed will cause severe problems in tracking the data. Also, the tracking of the photo-detecting assembly with respect to the spiral or concentric data track is of an indirect nature and can introduce errors and inherent unreliability. Further, only a single television scanline is disposed on each data track, thereby requiring a relatively high optical scanner speed. In this regard, the relatively low illumination efficiency of the tiny apertures of the Nipkow disk, in conjunction with the required relatively fast scan, limits the signal level which will be achievable using this scheme.
It is an object of the present invention to provide a system which overcomes problems of the prior art as set forth, and further provides a generally improved technique of data disk recording and reproducing.